Long-term slip rate of Chaochou fault


Chapter 3 Long-term slip rate of Hsinchu fault


 Long-term slip rate of Shanchiao fault (north segment)


Long-term slip rate of Luyeh fault


Long-term slip rate of Juisui fault











Long-term slip rate of Hsinchu fault

        This study we infer the probable surface fault trace by attitudes and lithology change in the outcrops and core-boring data in Touchien River site.(figure.1) The cross-section constructed by 7 boreholes give us the information about the geology underground, and there are 3 different stratigraphic units distinguished.(figure. 2) Unit A is a Holocene-recent river fluvium or colluvium in the landward area, and present a sand and mud facies of tidal environment near the coast. Unit B is a weathered gravel bed contains some thick sand bed. It is dated > 50,000 yr BP and inferred as Late Pleistocene fluvial deposit. Unit D is the Shianshan sandstone of Toukoshan Formation, it characterize as mudstone with thin sandy layers and occasionally contains sandstone or conglomerate several meters in thickness. The 3 units are tilted and violently sheared near the fault zone, the bedding dip ranges from 30-60º. Away from the fault zone the bedding display gentle dips to horizontal, that’s just similar to the phenomenon observed in the outcrop in Touchien River. In Touchienhsi no. 1-5 core-borings the bedding dips 50-70º. But in Hsinchu no.1 core-boring in more north side, the thickness of unit B increases and the bedding dip of unit D decrease to < 10º. Shearing is weaken and dip of shear plane also decrease to 20-30º. As present by the basement offset and suddenly change of dip angle of bedding and shear plane, we infer the surface trace of Hsinchu fault to the west of the Hsinchu no.1 core-boring site.


        In the geomorphic profile near Chienkung elementary school the height difference of lateritic terrace across the fault is ~30 m., we estimate the uplift rate of the Hsinchu fault by the dating > 50,000 yr BP and give the rate to < 0.6mm/yr.(figure. 3) From the borehole cross-section the unconformity between unit B and basement has a 60 m offset, so the rate is up to < 1.2 mm/yr. In the footwall area, we dated a tidal environment sediments in the 16.5 m depth of Nanliao borehole as 8850-9230 yr BP, and we estimate the uplift rate of the footwall block of the Hsinchu fault as 2.8±0.6 mm/yr.

Figure. 1 Core-boring sites and cross-section profiles in Hsinchu area.



Figure.2 Cross-section of core-boring data in Touchien river site.



Figure.3 Cross-section of core-boring data in C-C’ profile.